It is quite likely the EEPROM needs a slightly different configuration to enable the RJ45 port after all the components are added back.

I was going to say its not worth the effort and just buy another one with 10baseT but... 25€! thats like NZ$40! How are they that expensive! I've got like 120 of the things just sitting in a box - not that long ago they were like modems. People were just throwing them out.

Anyway, I don't see any mentions of firmware after a quick glance at the data sheet. There is a media selection parameter in EPROM which you would need to change - I expect you should be able to do this with the config utility for the card. Would be interesting to see if the utility gave you twisted pair as an option on this card - if it does then you'd probably get away with just adding the RJ45 jack, filtering and isolation components. To know what components are right for this particular card you'd need to find a decent photo of another card that is identical aside from the presence of RJ45.

As an example, I've got this one which uses the same chip but is RJ45 only. But the Valor SF1012 (which is providing the isolation transformer, low pass filter and choke) wouldn't fit your card:

Your card looks almost as mine, but yes that chip is different, Valor has 20 pins and my card has 16 pin slot and SMD components around it are a bit different.

So far I've found this

This looks to be the same card, but fully populated. It has 20F001N instead of valor chip, that one has fewer pins. I'll have to look if I can find better (topdown) image.

Today I've bought another card, this one has RJ45 and it cost me 23€, this one was cheapest 😬. That one is going into 486 to make file copying easier. BNC card (actually two) was intended to be just host for XTIDE so no problem there, but if there's an option to "upgrade" to RJ45 why not 😀.

If you don't mind the tinkering and really find all the correct components, I'd say it's worth a try.
PnP cards back then came with a setup software for DOS on the floppy that would usually let you set things like half/full duplex or medium type like BNC/10baseT/auto detect.
So chances are, it will work right away or with that setup tool or Win95 should be able to access the same.
These things were produced in such copious amounts that skipping the RJ45 part on a batch really could save a buck.

That being said - you should not rely on "buy it now" prices on Ebay. Those aren't realistic.

I could find several past auctions below 10 € for some kind of RJ45 ISA NIC. As low as 3.50 €:
https://www.ebay.de/itm/Netzwerkkarte-10-Mbit … A-/224804763959
The typical 3com etherlink III combo card should be ok around ten.

If on a budget, you need some patience. But NICs are really, really abundant.

davidrg wrote on 2022-04-21, 10:42:

I was going to say its not worth the effort and just buy another one with 10baseT but... 25€! thats like NZ$40! How are they that expensive! I've got like 120 of the things just sitting in a box - not that long ago they were like modems. People were just throwing them out.

I was thinking the same at first - why not just use a 3com Etherlink III with RJ45, one of those you use to keep the windows open or level that old table 😉

I've been checking ebay for ISA RJ45 cards for month and a bit but I either miss them or it's currently not the season for them 🤣. And one has to be careful not to buy ISDN adapter 😁.

Cheapest one I found was this one for 23€ I bought today. btw. that's with shipping, it's 15€ without shipping. These two BNC only cards were from Germany, I paid about 6€ for two of them and 12€ for shipping. Shipping is what drives the price up, if people even want to ship to Croatia. Seller from your link doesn't ship to Croatia.

Currently this is the cheapest one on offer for me, shipping is 9,90€.

First I'll look if I can find this setup software for this card. If I can't find any then it's a moot point as I can't reconfigure it 😁

Solo761 wrote on 2022-04-21, 12:40:

Your card looks almost as mine, but yes that chip is different, Valor has 20 pins and my card has 16 pin slot and SMD components around it are a bit different.

I suspect both are probably just adjusted versions of some reference design from National Semiconductor. I've got about a dozen cards with a "National Semiconductor" sticker on them like these, some with BNC only and others with BNC+AUI. They're more similar than not to the other cards:

I'd guess differences between cards with this chip probably just come down to cost or availability of components when the card was designed.

Version of my card that comes with RJ45 uses 20F001N filter, these are available on sites like aliexpress. I just need to confirm SMD component values. Capacitors are probably standard 0.1 uF ceramics, for resistors I'll need to either find datasheet to see what are recommended values or find high res photos of cards that use it and deduce from that. Like this one

download/file.php?id=94587&mode=view

Solo761 wrote on 2022-04-21, 20:25:

Seller from your link doesn't ship to Croatia.

That was just an example. I can imagine, Croatia is a much smaller domestic market for these things. Sometimes we Germans forget that we're not the USA, but neither are we a small country.

Shipping costs, in my experience with domestic shipping, many people are just stupid and/or lazy with choosing a shipping option. I mean, a NIC is really a small and light part. I gets even smaller and lighter once one removes the bracket, that almost reduces it to a standard letter.
So, success varies, but oftentimes I can persuade the seller to offer a cheaper option based on my own research.
I realize that Croatia is still not in the Schengen Area. But technically, I can get a ISA card from Munich as a letter for 1.60 € which is 500 km but Munich to Zagreb is only 400 km.
So, if at all possible, the market should figure that out somehow.
Just ordered a motherboard from abroad some weeks ago - came from Hungary for 10 €. But from Germany to x is probably more expensive, German deregulation efforts being what they are.

Solo761 wrote on 2022-04-21, 20:25:

First I'll look if I can find this setup software for this card. If I can't find any then it's a moot point as I can't reconfigure it 😁

Unless your card is some really major brand or you're extremely lucky, you'll find the DOS tool for the same chip, at best. But, as I wrote above, chances are that a) the card is "auto sensing" the correct medium anyway or b) any PNP OS like win95 etc, at least with generic drivers for the chip, will be able to handle that.

Cuttoon wrote on 2022-04-22, 16:38:

Solo761 wrote on 2022-04-21, 20:25:

First I'll look if I can find this setup software for this card. If I can't find any then it's a moot point as I can't reconfigure it 😁

Unless your card is some really major brand or you're extremely lucky, you'll find the DOS tool for the same chip, at best. But, as I wrote above, chances are that a) the card is "auto sensing" the correct medium anyway or b) any PNP OS like win95 etc, at least with generic drivers for the chip, will be able to handle that.

Drivers are easy (datasheet says "Software compatbile with Novell's NE2000/Plus industry standard Ethernet Adapters") but yeah, the setup program is going to be a challenge. I've done some digging on the internet archive and it looks like National Semi never publicly provided drivers for these things - just documentation on how to write drivers. I have found a driver package for the Octek ETHERNET 2000+3 v1.3+ DP83905-based card which appears to include a setup utility built by National Semi so possibly drivers and software were available on request or packaged with an evaluation board.

While digging I grabbed a copy of all of Nationals documentation for the chip - everything needed to build a brand new card (or I guess understand how an existing card works) should now be archived here: https://ftp.zx.net.nz/pub/doc/NationalSemiconductor/DP83905/. AN-875.pdf describes the evaluation board which I imagine most of these cards are pretty closely based on.

Cuttoon wrote on 2022-04-22, 16:38:

That was just an example. I can imagine, Croatia is a much smaller domestic market for these things. Sometimes we Germans forget […]
Show full quote

That was just an example. I can imagine, Croatia is a much smaller domestic market for these things. Sometimes we Germans forget that we're not the USA, but neither are we a small country.

Shipping costs, in my experience with domestic shipping, many people are just stupid and/or lazy with choosing a shipping option. I mean, a NIC is really a small and light part. I gets even smaller and lighter once one removes the bracket, that almost reduces it to a standard letter.
So, success varies, but oftentimes I can persuade the seller to offer a cheaper option based on my own research.
I realize that Croatia is still not in the Schengen Area. But technically, I can get a ISA card from Munich as a letter for 1.60 € which is 500 km but Munich to Zagreb is only 400 km.
So, if at all possible, the market should figure that out somehow.
Just ordered a motherboard from abroad some weeks ago - came from Hungary for 10 €. But from Germany to x is probably more expensive, German deregulation efforts being what they are.

Shipping fees are generally issue, not only on ebay, also shipping from online stores, not only from people. I guess it is what it is, I doubt Schengen will change anything in regards to this. (Coincidently, I'm a programmer currently working on goverment systems and implementing Schengen "rules" 😅)

Shipping costs are probably lower than stated, but take it or leave it. Five to six years ago most people wouldn't even ship outside of Germany and/or would except payment only to bank accounts which added additional cost of arround 5-6€ when paying to foreign bank account. Nowadays luckily it's paypal so (for buyer at least) that's it.

Cuttoon wrote on 2022-04-22, 16:38:

Unless your card is some really major brand or you're extremely lucky, you'll find the DOS tool for the same chip, at best. But, as I wrote above, chances are that a) the card is "auto sensing" the correct medium anyway or b) any PNP OS like win95 etc, at least with generic drivers for the chip, will be able to handle that.

I found something, not this card specific, but at least it's chip specific so it might work

https://www.driverguide.com/driver/detail.php?driverid=67738

Ordered filter chips (if you can call them that, it's basically few coils in a package...) for $8 so we'll see when they arrive in a month or so... Only problematic part are SMD components value. Capacitors should be standard 0,1 uF, but resistors are problematic. I haven't found clear high res image of this specific card, and of the ones that use same filter chip most have less or even none of these components, main chip is hooked directly to filter chip and on the other side to RJ45. We'll see...

davidrg wrote on 2022-04-22, 23:53:

While digging I grabbed a copy of all of Nationals documentation for the chip - everything needed to build a brand new card (or I guess understand how an existing card works) should now be archived here: https://ftp.zx.net.nz/pub/doc/NationalSemiconductor/DP83905/. AN-875.pdf describes the evaluation board which I imagine most of these cards are pretty closely based on.

Thanks! I'll check it out, maybe there'll be some info on these SMD components that I'm missing 😀. Maybe they'll requirements of DP83905 chip and not filter/transformer part.